In recent years, an optical image measuring technique of forming images that show the surface morphology and internal morphology of measured objects by using a light beam from a laser light source or the like has attracted attention. Unlike an X-ray CT apparatus, the optical image measuring technique is noninvasive to human bodies, and is therefore expected to be utilized more particularly in the medical field and biological field.
Japanese Unexamined Patent Application Publication No. Hei 11-325849 discloses a device to which the optical image measuring technique is applied. This device has such a configuration that: a measuring arm scans an object by a rotary deflection mirror (a Galvano mirror); a reference arm is provided with a reference mirror; and an interferometer is mounted at the outlet to analyze, by a spectrometer, the intensity of an interference light of light fluxes from the measurement arm and the reference arm. Moreover, the reference arm is configured to gradually change the light flux phase of the reference light by discontinuous values.
The device of Japanese Unexamined Patent Application Publication No. Hei 11-325849 uses a technique of so-called “Fourier Domain OCT (Optical Coherence Tomography).” That is to say, the device radiates a low-coherence light beam to a measured object, superposes the reflected light and the reference light to generate an interference light, and acquires the spectral intensity distribution of the interference light to execute Fourier transform, thereby imaging the morphology in the depth direction (the z-direction) of the measured object.
Furthermore, the device described in Japanese Unexamined Patent Application Publication No. Hei 11-325849 is provided with a Galvano mirror that scans with a light beam (a signal light), and is thereby configured to form an image of a desired measurement target region of the measured object. Because this device is configured to scan with the light beam only in one direction (the x-direction) orthogonal to the z-direction, an image formed by this device is a two-dimensional tomographic image in the depth direction (the z-direction) along the scanning direction (the x-direction) of the light beam.
Japanese Unexamined Patent Application Publication No. 2002-139421 discloses a technique of scanning with a signal light in the horizontal direction and the vertical direction to form a plurality of two-dimensional tomographic images in the horizontal direction, and acquiring and imaging three-dimensional tomographic information of a measured range based on the tomographic images. As the three-dimensional imaging, for example, a method of arranging and displaying a plurality of tomographic images in the vertical direction (referred to as stack data or the like), and a method of executing a rendering process on a plurality of tomographic images to form a three-dimensional image are considered.
Japanese Unexamined Patent Application Publication No. 2007-24677 and Japanese Unexamined Patent Application Publication No. 2006-153838 disclose other types of optical image measuring devices. Japanese Unexamined Patent Application Publication No. 2007-24677 describes an optical image measuring device that images the morphology of a measured object by scanning the measured object with light of various wavelengths, acquiring the spectral intensity distribution based on an interference light obtained by superposing the reflected lights of the light of the respective wavelengths on the reference light, and executing Fourier transform. Such an optical image measuring device is called a Swept Source type or the like.
Further, Japanese Unexamined Patent Application Publication No. 2006-153838 describes an optical image measuring device that radiates a light having a predetermined beam diameter to a measured object and analyzes the components of an interference light obtained by superposing the reflected light and the reference light, thereby forming an image of the measured object in a cross-section orthogonal to the travelling direction of the light. Such an optical image measuring device is called a full-field type, en-face type or the like.
Japanese Unexamined Patent Application Publication No. 2008-289579 discloses a configuration in which the OCT technique is applied to the ophthalmologic field. Before the optical image measuring device was applied to the ophthalmologic field, a fundus oculi observing device such as a retinal camera had been used (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 9-276232).
A fundus oculi imaging device using the OCT technique has a merit that images at various depths can be selectively acquired, as compared with a retinal camera that images the fundus oculi surface. Furthermore, the fundus oculi imaging device has a merit that images with higher definition can be obtained, as compared with a retinal camera. By utilizing such OCT technique, contribution to increase of the diagnosis accuracy and early detection of a lesion are expected.
For conventional optical image measuring devices, generally, imaging is performed with the steps shown in FIG. 16. As an example, cases in which a fundus examination is performed using a device shown in Japanese Unexamined Patent Application Publication No. 2008-289579 are explained below. First, by operating a control lever, alignment of an optical system with respect to a subject's eye is performed (S101). This operation is performed, for example, by projecting bright points to the subject's eye using an alignment optical system and operating the control lever, so as to dispose the bright points that are displayed on the screen inside a bracket-shaped scale.
Next, the optical system is brought into focus with respect to the region of interest of the subject's eye (for example, the macular area, optic papilla, etc.) (S102). This operation is performed, for example, by projecting a focus target with a certain optical system and operating the focus handle. More specifically, it is performed by projecting split bright lines made of two linear bright lines as the focus target, and operating the focus handle such that the two linear bright lines are disposed on one line.
When focus is completed, search and display of a coherent image is performed (S103). This operation is to display a coherent image of a desired depth position of the fundus oculi by adjusting the optical path length of the reference light. At this time, the optical path length is adjusted so as to increase the image quality of the desired depth position. Moreover, adjustment of the optical path length may be performed manually by an operator, or it may be performed automatically by obtaining and analyzing the coherent image.
Next, by pressing a predefined button, auto-tracking is started (S104). Auto-tracking is a technology in which a light beam (signal light) is controlled to track movement of the subject's eye, so as to dispose the region of interest in nearly the middle of the coherent image. This technology is, for example, disclosed in Japanese Unexamined Patent Application Publication No. 2008-342, Japanese Unexamined Patent Application Publication No. 2008-343, Japanese Unexamined Patent Application Publication No. 2008-154725 and Japanese Unexamined Patent Application Publication No. 2008-154726.
While performing auto-tracking, at the desired timing, the operator presses the imaging switch (S105). In response to this, the device obtains a coherent image (S106), and furthermore, takes fundus oculi images (S107).